In hospitals and laboratories, tissue piece treating apparatuses, in each of which tissue pieces are automatically fixed, dehydrated, degreased, replaced and embedded in paraffin, are used for producing microscopic specimens of tissue pieces taken from living bodies.
For example, a conventional tissue piece treating apparatus is disclosed in the following Patent Document 1, and the apparatus is shown in FIG. 9.
In the tissue piece treating apparatus shown in FIG. 9, a main body of the apparatus includes: a processing chamber 102 accommodating baskets 100, in which tissue pieces are inserted; a plurality of chemical tanks 104a-104e being mounted on a rack and storing chemicals, with sequentially different concentrations, for performing immersion treatment of the tissue pieces in the baskets 100; and paraffin tanks 106a and 106b accommodated in a heat-retaining chamber 106. Temperatures of the chemicals in the chemical tanks 104a-104e are 104a<104b<104c<104d<104e. 
Each of the chemical tanks 104a-104e and the paraffin tanks 106a and 106b is connected to a rotary valve 108 provided to the main body as a selection valve, and the rotary valve 108 is connected to the processing chamber 102 via an open/close valve 110.
With this structure, each of the chemical tanks 104a-104e and the paraffin tanks 106a and 106b is selectively connected to the processing chamber 102 by the rotary valve 108.
Further, inner pressure of the processing chamber 102 is increased and reduced by a pump 112, and the chemical or paraffin can be supplied to the processing chamber 102 from one of the chemical tanks 104a-104e and the paraffin tanks 106a and 106b, which is selected by the rotary valve 108.
The chemical or paraffin, which has been supplied to the processing chamber 102 and contacted the tissue pieces in the basket 100, is returned to the original tank by increasing the inner pressure of the processing chamber 102.
Since the rotary valve 108, the open/close valve 110 and the pump 112 are controlled by a control section 114, the tissue pieces can be immersed in the predetermined chemicals and the paraffin according to predetermined treatment sequence, which has been previously stored in the control section.
In the tissue piece treating apparatus shown in FIG. 9, an external tank 116 is located outside of the main body. An unused new chemical for treating the tissue pieces is stored in the external tank 116. The external tank 116 is connected to the rotary valve 108.
When the chemicals stored in the chemical tanks 104a-104b are used for the immersion treatment of the tissue pieces several times, each of the chemicals stored in the chemical tanks 104a-104b is transferred to the chemical tank in which the chemical, whose concentration is lower than and proximate to that of the chemical to be transferred, has been stored.
In the transferring process, firstly the chemical tank 104a, in which the chemical used for the immersion treatment of the tissue pieces the most times, including moisture from the tissue pieces and having the lowest concentration is stored, is detached from the main body, a vacant chemical tank 104a is attached thereto, and the chemical stored in the chemical tank 104b is transferred to the vacant chemical tank 104a via the rotary valve 108, the open/close valve 110 and the processing chamber 102.
Further, the chemical stored in the chemical tank 104c is transferred to the vacant chemical tank 104b via the rotary valve 108, the open/close valve 110 and the processing chamber 102. Namely, the chemicals are transferred to the adjacent chemical tanks as well, and finally the chemical tank 104d is evacuated.
The new chemical stored in the external tank 116 is transferred to the vacant chemical tank 104d via the rotary valve 108, the open/close valve 110 and the processing chamber 102.
Patent Document 1: Japanese Laid-open Patent Publication No. 2001-124679